1. Field of the invention
The present invention relates generally to a dubbing apparatus, and more particularly to a synchronizing circuit for a playback unit and a recording unit in a dubbing apparatus.
2. Description of the prior art
As well known, cassette tapes have merits of being compact in size and easy to handle, compared to conventional so-called open tapes. Due to the compactness and the handiness of the cassette tapes, cassette tape recorders have been popular for a long time in the audio field and a variety of functions have been recently developed for such equipment. For example, double cassette tape recorders, i.e., combination apparatus of two cassette tape drive mechanisms in a single body (hereafter referred to as double cassette tape recorders) are widely used in the portable equipment field. The double cassette tape recorders are convenient for dubbing from a recorded tape on one tape drive mechanism in the playback (PLAY) mode to an unrecorded tape on the other tape drive mechanism in the recording (REC) mode.
In addition, tape recorders have been developed which have their various operation modes logically controlled by microprocessors. In the tape recorders, so-called logic-control type tape recorders, operation keys for manually commanding the various operation modes are constructed to electrical soft-touch switches. Then, when any operation key of the soft-touch switch is depressed by an operator, the microprocessor activates a solenoid plunger in the tape recorder in response to the depression of the key. Then the solenoid plunger drives a playback magnetic head, and a pinchroller to their driving positions. Or the solenoid plunger drives the tape drive mechanism of the tape recorder so that a cassette tape is driven in the PLAY mode, the REC mode, a fast forward (FF) mode or a fast rewind (REW) mode. Therefore, the logic-control type tape recorders are easy to operate and simple in mechanism. The logic-control system has also been adopted to double cassette tape recorders, since the logic control system is especially suited for performing various complicated functions of the double cassette tape recorders and also for simplifying their complicated mechanisms. In the double cassette tape recorders of the logic-control type, dubbing is also performed by simply depressing a single key mounted on the front panel of the double cassette tape recorder.
The logic-control system consumes a tolerable large amount of power, because the solenoid plunger requires a large current to drive the tape drive mechanism. In addition, in conventional double cassette tape recorders, the tape drive mechanisms are simultaneously operated into the PLAY mode and the REC mode for dubbing. Therefore, a tolerable large amount of current flows for activating at least two solenoid plungers at the start of dubbing, but in other times, e.g., during a steady state of dubbing, during the PLAY mode etc., a relatively small current flows for driving the tape drive motors. Therefore, the conventional double cassette tape recorders of a battery driven portable type (hereafter referred to simply as portable double cassette tape recorders) must be equipped with a battery of a large power capacity, which may supply sufficient currents for the solenoid plungers of the respective tape drive mechanisms, at the start of dubbing. Therefore, it has been desired to reduce the amount of current required by the double cassette tape recorders, at the start of dubbing.